X-rays have been widely utilized in medical diagnostics as an imaging tool (i.e., radiography). In conventional radiography techniques, an image of an object's internal structures are obtained by interposing the object being imaged between a radiation source and an image recording medium. Exemplary image recording media include, but are not limited to, a film that responds to electromagnetic radiation, and a phosphor plate that utilizes concepts of fluoroscopy.
X-ray imaging techniques often include placing an object to be imaged between a high energy electromagnetic radiation source and an image recording medium. As radiation from the radiation source passes through the object, it is absorbed at varying levels by the internal structures of the object. Upon exiting the object, the radiation impinges on the image recording medium with an intensity related to the attenuation of the radiation caused by the different absorption characteristics of the internal structures of the object being imaged. The impinging radiation causes a change in the image recording medium that is proportional to its intensity, thereby storing information about the internal structure of the object. The image recording medium may then be processed to recover the stored information by, for instance, converting it into digital form using various computer radiography (CR) techniques.
X-rays also have been used in radiotherapy (RT) applications as a treatment to fight diseases such as cancer. Radiotherapy often includes both an initial imaging step and a treatment step. The purpose of the initial imaging step, commonly referred to as radiotherapy planning, is to obtain an image of a patient's internal organs without undue exposure to X-ray radiation. Accordingly, such planning images are often obtained at low energy radiation levels, typically on the order of tens to hundreds of kilo-electron-volts (KeV). The planning images then guide the radiation treatment process and facilitate determining various properties of the high energy radiation to be used subsequently during treatment. The planning stage may, for example, ensure that a proper dose of radiation is provided to the patient and applied only in the area of the intended anatomical target.
Radiotherapy treatment also may involve an additional imaging step, referred to as portal imaging, to confirm that the high energy radiation for treatment is properly positioned to expose the intended anatomical target. Portal imaging typically involves first briefly exposing the patient to high energy radiation (typically on the order of mega-electron-volts or MeV) to obtain a faint image of internal organs of the patient to be used as a reference image. The patient is subsequently covered with a radiation shield having a port that permits the passage of radiation through the shield to a small targeted region of the patient. The patient then is exposed again through the port to generate a “portal image,” which is subsequently superimposed over the reference image to verify that the port is properly aligned with the radiation source and the intended anatomical target.
From the foregoing examples, it should be appreciated that radiography may include employing radiation having different energy levels for different types of imaging applications, or within various steps of an imaging process (e.g., in the planning and treatment stages of radiographic therapy). However, the response of different types of conventional image recording media generally varies with different energy exposure levels of radiation.
For example, phosphor plates store energy when impinged by radiation. This energy can later be released by scanning the plate with a laser to cause the phosphors in the plate to fluoresce. However, at higher energy levels, such as those used during radiotherapy treatment (e.g., on the order of MeV), the phosphor plate properties are such that high energy photons have a very low probability of interacting with the phosphor plate atomic lattice. Stated differently, the phosphor plate appears increasingly transparent to higher energy radiation and may not be suitable for imaging applications involving high energy radiation levels. Accordingly, phosphor plates generally are more suitable for imaging applications involving low energy radiation levels on the order of KeV (e.g., radiation levels used during radiotherapy planning and other diagnostic imaging tasks).
As a result of the foregoing, in a conventional radiotherapy treatment process involving both planning and portal imaging, a phosphor plate may be used during the planning stage, but not during the portal imaging or treatment stages, due to the higher energy level of radiation used during portal imaging. However, phosphor plates have a generally desirable characteristic in that they may be reused for multiple exposures. Accordingly, some conventional radiotherapy processes may require different types of recording media to be employed at the different imaging stages of the imaging process (e.g., phosphor plates during the planning stage and film during the treatment stage). However, using various media may create problems associated with aligning the images stored on different media and generally complicates the imaging process, making it difficult and time consuming.
Radiotherapy, for example, may be further complicated due to the different handling apparatus that may be required for the various stages. A handling apparatus adapted for one type of image recording media may be unsuitable for another increasing the types of equipment that must be maintained and complicating the image acquisition process. For example, in some radiography applications, an image recording medium may be encased in a protective cassette before and during the imaging process. The term “cassette” refers generally to any of various casings, cartridges or containers adapted to hold other material, and more particularly, material that may benefit from protection and/or material susceptible to damage from direct handling, contact or exposure.
For example, a cassette may be formed as a rigid encasement providing a shell that can withstand the weight of a patient, rough handling, accidental falls, etc. In addition, the cassette typically includes an interface (e.g., a window) that permits radiation to interact with the image recording medium. Once the medium has been exposed to some form of radiation, it is typically removed from the cassette and loaded into an image acquisition system for further processing. For purposes of this disclosure, an image acquisition system refers generally to any apparatus or combination of apparatus that performs processing on the image recording medium after it has been exposed.
A reusable recording medium such as a phosphor plate may be placed into and out of a cassette several times over the life of the medium. For example, in some conventional computer radiography (CR) applications, a phosphor plate in a cassette is exposed to radiation and then the plate is loaded into a CR image reader, which scans the plate to produce a digital image. The phosphor plate is then reloaded into the cassette after image acquisition and may be reused to obtain further images. This process may be repeated several times to accommodate multiple exposures and image acquisitions.
In many cases, one or more of the acts of removing and replacing the image recording medium into the cassette, and loading and unloading the image recording medium into an image acquisition system, are performed manually. That is to say, the acts are carried out at least in part by an operator. However, image recording media, especially reusable media such as phosphor plates, generally are vulnerable to damage during manual handling. In addition, manually removing and replacing image recording media to and from the cassettes and manually loading and unloading the media into and out of the image acquisition system is often inconvenient and time-consuming. In particular, much care must be taken not to scratch or otherwise damage the medium during the process and to ensure that the medium has been properly loaded into the image acquisition device and cassette, respectively.
In view of the foregoing, it may be appreciated that some image recording media, and in particular phosphor plates, generally are useful for imaging applications over particular energy ranges of radiation exposure, and may be used for multiple exposures and subsequent image acquisition. Additionally, some image recording media, such as phosphor plates for example, are generally susceptible to some degree of damage during handling, especially over multiple uses where possible.